1. Field of the Invention
The present invention relates to a hybrid integrated circuit device with a built-in microcomputer and, in particular, to a hybrid integrated circuit device provided with a non-volatile memory which feeds data to the microcomputer, and which can be treated as an electronic part which functions independently.
2. Description of the Background Art
An EPROM element with an ultraviolet light irradiation window provided in its surface by which it is possible to erase stored data written on a chip by ultraviolet irradiation and to rewrite into that memory is preferably used in various types of electronic devices. Usually, these EPROM elements are detachably mounted on a printed board for subsequent rewriting. Most of these EPROMs are mounted together with a control- or drive-integrated circuit on a printed board. For electronic devices which must be small and light-weight, a technique known as "chip-on-board" is adopted, wherein a semiconductor integrated circuit (IC) chip is directly mounted on a printed board, and after the required wiring is implemented, the IC chip and the wiring section are covered with a synthetic resin. However, in an electronic device for which an EPROM element is required, because it must be possible to erase the stored data by directing ultraviolet light onto the EPROM element, and to rewrite into the element, the chip-on-board technique whereby an EPROM chip is mounted directly on a printed board and covered with a synthetic resin cannot be adopted. For this reason, in an electronic device for which an EPROM element is required, there is no other choice but to use an EPROM element incorporated in a SADIP-type package. This is an obstacle to an small-size, light-weight unit.
FIG. 1 is a perspective view of an EPROM substrate, which explains the mounting structure of a conventional EPROM element. One part of an EPROM element 74 is shown in section.
A plurality of through-hole terminals 73 and a plurality of male connector terminals 85 made of a conductive material as well as a conductive wire pattern 71 connecting these terminals are formed on the main surface of an insulating substrate 72 made from glass-epoxy resin or other similar material. An external conductive lead 78 of the EPROM element 74 incorporated into a SADIP-type package is inserted through and electrically connected by soldering to the through-hole terminal 73, and is mechanically secured to the insulated substrate 72.
The EPROM element 74 is provided with a ceramic header 75 and a ceramic cap 76. The external conductive lead 78 is bonded to the header 75 using a glass material with a low melting point. An element mounting section 80 which is produced from a sintered gold paste made up of a large quantity of gold powder mixed with glass is also bonded directly to the header 75, or indirectly to the header 75 through the low melting point glass material which is extended to the element mounting section 80. An EPROM chip 81 with an ultraviolet emitting surface on the top is mounted on the element mounting section 80. An electrode of the chip 81 is connected to the external conductive lead 78 with a fine metal wire 82. The cap 76 is a cover member provided with a window 83 vis-a-vis the ultraviolet emitting surface of the EPROM chip 81. The cap 76 is bonded to the header 75 using a low melting point glass, and seals the EPROM chip 71 which is positioned on the header 75. The EPROM substrate having the above structure is formed independently of the main circuit print board. The EPROM element 74 is connected to a microcomputer or the like mounted on the main circuit print board. This connection is made through the external conductive lead 78, the through hole terminal 73, the conductive wire pattern 71, a male connector terminal section 85, and a female connector (omitted from the drawings).
The external form of a package when such a conventional EPROM element mounting method is used is extremely large relative to the EPROM chip 81. In addition to a large plan area, the height of the elements is also several times the height of the chip. This is a severe handicap in providing a thin printed board. After the external conductive lead is inserted into the through hole terminal 73, the EPROM element must be secured by solder or the like. In addition, a particularly troublesome drawback is the fact that, before mounting on the insulated substrate, the EPROM element must once be assembled in the package. Because the EPROM element is provided with an ultraviolet emitting window, the package is assembled in a SADIP-type package made from a ceramic and, because this package is sealed using low melting point glass, a high temperature (400.degree. C. to 500.degree. C.) sealing process must be adopted. If the electrode (aluminum) of the EPROM chip and the fine metal wire which connects the electrodes (aluminum) of the EPROM chip to the external conductive lead are not made from the same type of material, an alloy is produced at the sealed section during the high temperature sealing process and the resistance of the wire increases. This can cause the wire to break. A fine aluminum wire is usually used to avoid this kind of trouble, but, in this EPROM chip, the earth electrode of the EPROM chip is wired to the mounting section of the chip which is formed with gold paste, because the substrate of the EPROM chip must bear earth potential. Here as well, a binary or multiple alloy reaction occurs between the gold in the gold paste and/or the metal in the metal foil or the like, and the aluminum. Because of this, a small silicon leaf covered with aluminum on the head referred to as a gland die, is attached to the chip mounting section formed from the gold paste, and the earth electrode of the EPROM is connected to the top of the gland die. The conventional mounting structure has many drawbacks accompanied by the above complicated process. Thus, the conventional mounting structure does not satisfy any of the requirements for small size, light weight, and low cost.
The EPROM mounting structure shown in FIG. 2 has been proposed to eliminate this type of problem. This mounting structure will now be explained with reference to the drawing.
An insulated substrate 86 made from a glass-epoxy resin or other similar material has a main surface 87 on which is formed a wiring pattern 88. A chip mounting area 89 which supports an EPROM chip 90 is provided on the insulated substrate 86. The wiring pattern 88 is routed on the main surface 87 from a point close to the chip mounting area 89 and is connected to a male connector terminal (omitted from the drawing). The EPROM chip 90 is mounted on the chip mounting area 89. A surface electrode of the EPROM chip 90 is connected to the wiring pattern 88 by a fine metal wire 92. The substrate of the EPROM chip 90 as well is connected to the mounted wiring pattern 88 by one strand of the fine metal wire 92. An ultraviolet transmitting window material 94 of the EPROM chip 90 is fixed on the ultraviolet-emitting surface 91 of the EPROM chip 90 through an ultraviolet transmitting resin 93 [for example, TX-978 (trademark), manufactured by Toray]. The window material 94 is made from a commonly known ultraviolet transmitting material such as quartz, transparent alumina, or the like. The top surface 95 of the window material 94 is a surface which introduces light to the ultraviolet-emitting surface 91 of the EPROM chip 90. The parts of the window material 94 other than the top surface 95, the fine metal wire 92, and the part connecting the fine metal wire 92 with the wiring pattern 88 are covered with a synthetic resin 96 [for example, MP-10 (trademark), manufactured by Nitto Denko Corp.]. If the base of the chip mounting area 89 of the substrate 86 is situated on a concave at about half the height of the substrate 86, it is possible to further reduce the combined thickness of the insulated substrate 86, the EPROM chip 90, and the window material 94, while formation of a floodgate by the synthetic resin 96 effectively prevents moisture from entering. The EPROM mounting structures shown in FIG. 1 and FIG. 2 are disclosed in Japanese Patent Laid-open No. 83393/1985 (H05K 1/18).
Because the EPROM chip is die-bonded to the printed board in the EPROM mounting structure shown in FIG. 2, the printed board is reduced in size by only the amount of reduction of the EPROM. However, because the microcomputer which is to be fixed near the EPROM chip and its peripheral circuit elements (not shown in FIG. 2) are fabricated as discrete electronic parts, the size reduction is hardly achieved, if the printed board on which the EPROM is mounted is viewed as a system. In addition, in the EPROM having the structure illustrated in FIG. 2, rewriting of program data onto the EPROM chip must be performed after the program data has been erased by exposing the printed board to ultraviolet light, by touching a write-in terminal, such as a probe or the like, to the conductive pattern extending from the EPROM chip. This entails a problem that because usual conventional ROM writers cannot be used, troublesome procedures are required for rewriting onto an EPROM.
With the EPROM mounting structure shown in FIG. 1, since the EPROM is detachably mounted on the main printed board, a conventional ROM writer can be used for writing. However, the circuits around the EPROM, i.e. the microcomputer and its peripheral circuit elements, such as LSIs, ICs, and the like, are constructed as discreet electronic parts in the same manner as in FIG. 2. This causes the printed board as well as the total system to be large in size, making it impossible to provide a small and light integrated circuit as the user requires. This is a major problem. In addition, an independent printed board for the EPROM element is required, and the wiring pattern 71 for connecting the EPROM element 74 to a microcomputer becomes very long, bringing about the problem that size reduction cannot be achieved.
With the EPROM mounting structures shown in FIG. 1 and FIG. 2, the complete system becomes large, as outlined above. In addition, because the conductive pattern which connects the EPROM and the peripheral circuit elements are exposed, reliability is lowered.
Furthermore, with the EPROM mounting structures shown in FIG. 1 and FIG. 2, because the EPROM and its peripheral microcomputer and circuit elements, such as LSIs, ICs, and the like are exposed, irregularities are formed on the upper surface of the substrate, reducing operability and making servicing difficult.